Dietary Influence on Body Fluid Acid-Base and Volume Balance: The Deleterious "Norm" Furthers and Cloaks Subclinical Pathophysiology

Distinguishing Low and High Water Consumers-A Paradigm of Disease Risk

A long-standing body of clinical observations associates low 24-h total water intake (TWI = water + beverages + food moisture) with acute renal disorders such as kidney stones and urinary tract infections. These findings prompted observational studies and experimental interventions comparing habitual low volume (LOW) and high volume (HIGH) drinkers. Investigators have learned that the TWI of LOW and HIGH differ by 1-2 L·d-1, their hematological values (e.g., plasma osmolality, plasma sodium) are similar and lie within the laboratory reference ranges of healthy adults and both groups appear to successfully maintain water-electrolyte homeostasis. However, LOW differs from HIGH in urinary biomarkers (e.g., reduced urine volume and increased osmolality or specific gravity), as well as higher plasma concentrations of arginine vasopressin (AVP) and cortisol. Further, evidence suggests that both a low daily TWI and/or elevated plasma AVP influence the development and progression of metabolic syndrome, diabetes, obesity, chronic kidney disease, hypertension and cardiovascular disease. Based on these studies, we propose a theory of increased disease risk in LOW that involves chronic release of fluid-electrolyte (i.e., AVP) and stress (i.e., cortisol) hormones. This narrative review describes small but important differences between LOW and HIGH, advises future investigations and provides practical dietary recommendations for LOW that are intended to decrease their risk of chronic diseases.

Mechanisms of Metabolic Acidosis-Induced Kidney Injury in Chronic Kidney Disease

Retrospective analyses and single-center prospective studies identify chronic metabolic acidosis as an independent and modifiable risk factor for progression of CKD. In patients with CKD, untreated chronic metabolic acidosis often leads to an accelerated reduction in GFR. Mechanisms responsible for this reduction include adaptive responses that increase acid excretion but lead to a decline in kidney function. Metabolic acidosis in CKD stimulates production of intrakidney paracrine hormones including angiotensin II, aldosterone, and endothelin-1 (ET-1) that mediate the immediate benefit of increased kidney acid excretion, but their chronic upregulation promotes inflammation and fibrosis. Chronic metabolic acidosis also stimulates ammoniagenesis that increases acid excretion but also leads to ammonia-induced complement activation and deposition of C3 and C5b-9 that can cause tubule-interstitial damage, further worsening disease progression. These effects, along with acid accumulation in kidney tissue, combine to accelerate progression of kidney disease. Treatment of chronic metabolic acidosis attenuates these adaptive responses; reduces levels of angiotensin II, aldosterone, and ET-1; reduces ammoniagenesis; and diminishes inflammation and fibrosis that may lead to slowing of CKD progression.